JPS6350662Y2 - - Google Patents

Description

[Detailed Description of the Invention] The present invention relates to a power supply device suitable for a talkie projector capable of recording and reproducing audio signals, and particularly for a talkie projector using a metal halide lamp as a light source.

Since metal halide lamps have particularly excellent color rendering properties and luminous efficiency, they are convenient for use as a light source for talkie projectors intended for public exhibitions. As a stabilized power source for stably lighting this type of metal halide lamp, it is preferable to use a switching regulator type power source that is highly efficient, compact, and can be built into a projector. However, in conventional switching regulator type power supplies, ripple components of the voltage and current obtained on the output side usually mix into the magnetic head of the audio signal recording/reproducing circuit, causing noise. This had a significant adverse effect on the recording and reproduction of audio signals. For this reason, in switching regulator type power supplies used in talkie projectors, a special noise prevention capacitor is connected to the output side to smooth the output voltage and current and remove ripple components. It is necessary to minimize the noise generation as much as possible.

By the way, while the above-mentioned noise prevention capacitor has the advantage of reducing ripple components on the output side of the power supply, it also reduces the impedance of loads connected to this output side, especially loads with negative resistance such as metal halide lamps. The following drawbacks arise with respect to changes in . In other words, in general, to ignite a metal halide lamp, the output state of the power supply device must be rapidly changed from an initial state of supplying a small current at a high voltage to a stable state of supplying a large current at a low voltage in response to changes in the impedance of the load. However, if a capacitor is connected in parallel with the metal halide lamp during such ignition, the output state of the power supply will not be able to follow the change in impedance of this load, and the metal halide lamp will often It becomes impossible to ignite.

For this reason, in the past, in order to prevent the generation of noise due to ripple components of the voltage and current on the output side of the power supply device for metal halide lamps, the capacitor described above was not provided, but instead was provided on the output side of the power supply device. Countermeasures were taken such as increasing the size of the chiyoke coil, but increasing the size of the chiyoke coil made the power supply itself larger, and the chiyoke coil alone could not sufficiently prevent the generation of noise. When the power supply device is integrated with the talkie projector, the influence of noise cannot be ignored, so incorporating the power supply device into the talkie projector has been accompanied by many difficulties.

In view of the above-mentioned points, the present invention prevents the noise generated in the audio signal recording/reproducing circuit etc. due to the ripple components of the voltage and current on the output side of the power supply device, and
Another object of the present invention is to provide a power supply device for a metal halide lamp that is large enough to be built into a talkie projector.

Hereinafter, one embodiment of the present power supply device will be described in detail based on the drawings.

In FIG. 1, a line voltage supplied between input terminals A and B is rectified and smoothed by a DC power supply circuit 1 and converted into DC, and this DC is applied to a switching regulator 2. This switching regulator 2 includes, for example, a chopping transistor 3 that periodically switches on and off applied direct current, a chopper control circuit 4 that controls the conduction period of this transistor 3, and a commutation diode 5. , and the smoothing coil 6, and the voltage on the output side of the coil 6,
In order to cause the chopper control circuit 4 to control the conduction period of the chopping transistor 3 according to the current, and to keep the output power constant, a resistor 7 for detecting the voltage on the output side of the chopping coil 6; 8, a voltage across the resistor 9 for detecting the output current, and a voltage for applying the voltage across the resistor 9 to the chopper control circuit 4, and a current feedback circuit. The output side of the switching regulator 2 is connected to a metal halide lamp 11 via a DC-AC conversion circuit 10 for alternating the polarity of DC at a constant cycle and applying it to a load. According to the configuration described above, it is possible to provide a power supply device that functions sufficiently for general lighting equipment, but in the power supply device with this configuration, there are many ripple components in the voltage and current on the output side, and this ripple component This mixes into the audio signal recording and reproducing circuit and causes noise, which has a significant adverse effect on the recording and reproducing of audio signals by the talkie projector.

Therefore, in the present device, in addition to the circuit configuration described above, the capacitor 12 for noise prevention is connected to the switching regulator in conjunction with the ignition operation of the metal halide lamp 11, and after a predetermined time delay from the ignition operation. A current detection circuit 13 for detecting a part of the output current of the transistor 3 is provided on the output side of the transistor 2 for connection control. This current detection circuit 13 is connected to a rectifying and smoothing circuit consisting of a diode 14 and a capacitor 15 for rectifying and smoothing a part of the output current of the transistor 3, and to the output side of this rectifying and smoothing circuit via a resistor 16. It is composed of a well-known delay relay 17, and the relay contact 17a of this delay relay 17 is closed after a predetermined time has elapsed after the relay coil 17b is energized by the output of the rectifying and smoothing circuit. The aforementioned noise prevention capacitor 12
After a predetermined period of time has passed after the metal halide lamp 11 is ignited, the switching regulator 2 is turned on.
Connect to the output side of the

The operation of the power supply device according to the present invention will be explained below.

When the lamp switch of the talkie projector is operated, the chopping transistor 3 is turned on or off by the chopper control circuit 4.
Therefore, the DC voltage obtained in DC power supply circuit 1 is
When V ₁ , the conduction period T _ON of the chopping transistor 3 and the
Corresponding to the cut-off period T _OFF , a voltage V _D having a pulse waveform with a peak value of V ₁ and a pulse width of T _ON is generated as shown in FIG. 2A. At this time, a current I _C with a waveform as shown in FIG. 2B flows through the collector of the chopping transistor 3, and a forward current with a waveform as shown in FIG. 2C flows through the commutation diode 5. As a result of the flow of _ID , the second
Current with relatively large ripple components as shown in Figure D
I _L flows. The current flowing through this choke coil 6 is applied to a metal halide lamp 11 via a DC/AC conversion circuit 10. At this time of ignition, the internal impedance of the metal halide lamp 11 changes rapidly as described above, but the inductance of the choke coil 6 prevents the sudden change in the current applied to the metal halide lamp 11, so that the metal halide lamp 11 is reliably ignited. be done.

On the other hand, a part of the collector current I _C of the stepping transistor 3 is smoothed by a rectifying and smoothing circuit consisting of a diode 14 and a capacitor 15 of the current detection circuit 13, and then passed through a resistor 16 to the delay relay 17. It is applied to relay coil 17b, and this relay coil 17b is energized. After a predetermined time has elapsed after the relay coil 17b is energized, the relay contact 17a is closed. For this reason,
The noise prevention capacitor 12 is connected in parallel to the output side of the switching regulator 2 after a predetermined period of time has elapsed since the collector current I _C of the transistor 3 started flowing by operating the lamp switch.
When this capacitor 12 is connected, the ignition of the metal halide lamp 11 has already been completed as described above, so the capacitor 12 for noise prevention is connected to the output side of the switching regulator 2 as described above. However, the metal halide lamp 11 does not go out, and by connecting this capacitor 12, the output current of the switching regulator 2 is smoothed, and the ripple component is extremely small as shown in Fig. 2 E. It is now possible to supply the current I _O to the metal halide lamp 11, and it is possible to prevent the generation of noise due to ripple components when recording and reproducing audio signals.

As is clear from the above explanation, the present power supply device ensures the lighting of the metal halide lamp connected to the output side of the switching regulator type power supply device, and furthermore, the voltage generated on the output side of the power supply device, Furthermore, since the ripple component of the current can be significantly reduced when the metal halide lamp is turned on, the power supply device of the present invention is extremely convenient for application as a power supply device for a talkie projector.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing the electrical configuration of one embodiment of the present power supply device, and FIG. 2 is an output signal waveform diagram showing output signal waveforms of each part of FIG. 1. DESCRIPTION OF SYMBOLS 1... DC power supply circuit, 2... Switching regulator, 3... Transistor, 4... Chopper control circuit, 5... Diode, 6... Choyoke coil, 11... Metal halide lamp, 12...
...Capacitor, 13...Current detection circuit.

Claims (1)

[Scope of utility model registration request] A transistor for intermittent output from a DC power supply circuit, a chopper control circuit for controlling the conduction period of the transistor, a diode for commutation,
and a smoothing coil, and a voltage and current feedback circuit for controlling the conduction period of the transistor according to the voltage and current on the output side of the coil, so that the output power is constant. In a power supply device for a talkie projector that supplies constant power to a metal halide lamp via a switching regulator, a part of the output current of the transistor is detected by a current detection circuit, and after starting the ignition operation of the metal halide lamp. . The power supply device for the talkie projector, characterized in that, after a certain time delay, a capacitor is connected in parallel to the output side of the switching regulator.